Power Quality &

Synchronisation

Ben Kemink

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Power Quality

What is the Quality of the Power Measurement?

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Subjects Covered

1. Definition of Electrical Power

2. The meaning of “T”

3. Should we select the Voltage or the Current input channel for Synchronization?

4. Is an Observation Time an alternative for “T”?

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Power Quality

Before discussing quality of power,

lets have a look at how do we

define the measurement of electrical power?

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Traditional

CONSTANT AVERAGE=0

Applied Voltage : u(t) = Upk.sin(t)

Resulting Current : i(t) = pk.sin(t+)

Amplitude=UrmsxIrms

p(t) = u(t) . i(t) =

= ½ . Upk . Ipk . cos( ) - ½ . Upk . Ipk . cos(2t+ )

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Definition of Average Power

dt.)t(1 T

0average p

TP

The most difficult task for the power meter is to find the period time T correctly!

Especially with distorted signals this can be very difficult.

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Traditional 50Hz

Amplitude=Urms x Irms

Vpk

Ipk

Pavg

Tp

Ti

Tu

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Zero Crossing?

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The zero crossing lasts at least for one acquisition interval. An uncertainty caused by time resolution.

Δt = resolution of Tperiod

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Current input channel is used for synchronization.

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What if the period is longer than the acquisition memory of the power meter?

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A too low Display Update Rate will not detect changes of short duration despite a high acquisition speed.

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Power Quality is first of all related to an accurate Power Measurement

Factors that influence the total error for power are:

Amplitude Frequency of the fundamental of the input signal Crest Factor of the input signal (BW) Crest Factor setting of the Power Meter Power Factor Temperature Use of filters Acquisition interval Acquisition Clock Stability

Correct Detection of Period Time “T”

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There is enough energy. The challenge is how to control it!

For Example:If of 1 gram uranium all atoms split, the heat

developed (energy) can make a water basin, 6 x 6 x 5 meter filled with water of 0 degrees Celsius, boil.

Source: Van Barnsteen naar Kernchemie, Dr. K.K. Darrow

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Three ways to control Electrical Power

1. The current is manipulated. Example: Switched Power Supplies, Resistors.

2. The voltage is manipulated.

Example: Pulse Width Modulated Power Inverters, Frequency Converters, Soft-starters, Thyristor Controlled Power Supplies, Inductive Cooking.

3. Both the voltage and the current are manipulated.

Example:Electronic Ballasts for Lighting

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1. Current Manipulation

Voltage

Current

Example: Switching Power Supply

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1. Current Manipulation

Voltage

Current

Power

example: Switching Power Supply, Voltage, Current & Power Harmonics

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2. Voltage Manipulation

example: Inductive Cooking

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2. Voltage Manipulation

example: 3-Phase Frequency Inverter Output

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2. Voltage Manipulation

example: Soft starter

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3. Voltage & Current Manipulation

WT1600

example: Lighting Industry, electronic ballast

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3. Voltage & Current Manipulation

example: 50kHz Electronic Ballast for TL

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Design engineers are very creative.

Summary

Today electric power consumption is controlled by high speed (switching) electronics.

To limit the negative side effects for others, new regulations are issued frequently to set new guidelines for design.

The definition of the average electric power has not changed, but the selection of the true repetition time T (period) requires special attention.

The power meter should allow the user to select the appropriate synchronisation source for the measurement calculations.

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The power meter should allow the user to select the synchronisation source for the measurement calculations.

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THANK YOU

QUESTIONS?